The present invention relates to polymer composite piezoelectric bodies suitable for piezoelectric devices, sensors, ultrasound probes, electric power generating devices, vibration-powered generators, and the like, as well as methods of manufacturing such piezoelectric bodies. The present invention is particularly directed to a polymer composite piezoelectric body having piezoelectric particles uniformly mixed by dispersion in a polymer matrix composed of cyanoethylated polyvinyl alcohol, and a method of manufacturing such a piezoelectric body.
Polymeric piezoelectric materials are those piezoelectric materials which have characteristics inherent to polymer materials, such as good flexibility, high-impact properties, ease of machining, and ability to have an increased area, which are high in power output constant (piezoelectric “g” constant) as compared with inorganic piezoelectric materials, and which are similar in acoustic impedance to the human body or water, so that their application to various sensors, or ultrasonic transducers such as an ultrasound probe and a hydrophone, vibration controllers (dampers), or to the vibration energy harvesting is expected nowadays. In such fields of application, those piezoelectric materials are sought which have a piezoelectric strain constant (“d” constant) as an index to the strain amount per unit electric field (signal sending ability) and a “g” constant as an index to the strength of electric field generated per unit stress (signal receiving ability) both favorable in magnitude, or are excellent in balance between the constants.
The polymeric piezoelectric materials are known to include piezoelectric polymers, namely, the polymers piezoelectric in themselves as typified by polyvinylidene fluoride (PVDF), which are low in “d” constant as compared with inorganic piezoelectric materials and, accordingly, cannot effect adequate performance if used for the above applications as a polymeric piezoelectric material.
On the other hand, the polymer composite piezoelectric which is obtained by using a polymer material as a matrix and mixing an inorganic piezoelectric into the polymer matrix to produce a piezoelectric composite is a piezoelectric allowed to have the above advantages typical of polymer materials and an excellent piezoelectric performance (“d” constant) of the inorganic piezoelectric in an effective manner. Polymer composite piezoelectrics are claiming attention as a piezoelectric variable in material design with different applications by changing the type of a polymer serving as a matrix, the type or composition of the inorganic piezoelectric, the connectivity, or the shape, or the blending ratio. In consequence, a variety of polymer composite piezoelectrics have been proposed (see Patent Literature 1, for instance).
As a matter of course, it is preferable that a piezoelectric with high piezoelectric performance is used for a polymer composite piezoelectric, so that use is chiefly made of lead-based piezoelectric materials having extremely high “d” constants, such as lead zirconate titanate (Pb(Zr,Ti)O3: PZT).
Patent Literature 1 discloses the electronic component material having good dielectricity, pyroelectricity and piezoelectricity that is obtained by forming a composite product by uniformly mixing by dispersion a ferroelectric substance consisting of ceramic particles with a perovskite-type crystal structure in a dielectric binder composed of cyanoethylated cellulose and/or cyanoethylated pullulan, and applying a specified voltage to the composite product.